This invention relates to a method and apparatus for filling and capping an acoustic ink printhead. More particularly, the invention is directed to a method and apparatus utilizing a capping element having a sealing element or gasket which is pushed against the orifice plate of an acoustic ink printhead when capping and filling. This traps a small volume of air around an array of orifices in the orifice plate forming an air cushion, enabling the printhead to be filled without any exiting of ink through the orifices.
While this invention is particularly directed to the art of acoustic ink printing (or AIP), and will thus be described with specific reference thereto, it will be appreciated that the invention may have usefulness in other fields and applications. For example, the invention may have application with any type of printhead where a constant flow of a pool of ink is utilized.
By way of background, it has been shown that acoustic ink printers which have printheads comprising acoustically illuminated spherical or Fresnel focusing lenses can print precisely positioned picture elements (pixels) at resolutions that are sufficient for high quality printing of complex images. Significant effort has gone into developing acoustic ink printing, see for example, U.S. Pat. Nos. 4,308,547; 4,697,195; 4,751,530; 4,751,534; 5,028,937; and 5,041,849, all of which are among many commonly assigned to the present assignee.
Although acoustic lens-type droplet emitters currently are favored, there are other types of droplet emitters which may be utilized for acoustic ink printing, including (1) piezoelectric shell transducers, such as described in Lovelady et al., U.S. Pat. No. 4,308,547, and (2) interdigitated transducers (IDTs), such as described in commonly assigned U.S. Pat. No. 4,697,195. Furthermore, acoustic ink printing technology is compatible with various printhead configurations; including (1) single emitter embodiments for raster scan printing, (2) matrix configured arrays for matrix printing, and (3) several different types of page and width arrays, ranging from (i) single row sparse arrays for hybrid forms of parallel/serial printing to (ii) multiple row staggered arrays with individual emitters for each of the pixel positions or addresses within a page width address field (i.e., single emitter/pixel/line) for ordinary line printing.
For performing acoustic ink printing with any of the aforementioned droplet emitters, each of the emitters launches a converging acoustic beam into a pool of ink, with the angular convergence of the beam being selected so that it comes to focus at or near the free surface (i.e., the liquid/air interface) of the pool. Moreover, controls are provided for modulating the radiation pressure which each beam exerts against the free surface of the ink. That permits the radiation pressure from each beam to make brief, controlled excursions to a sufficiently high pressure level to overcome the restraining force of surface tension, whereby individual droplets of ink are emitted from the free surface of the ink on command, with sufficient velocity to deposit them on a nearby recording medium.
A main attraction of acoustic ink printing is the ability to control droplet size based on the frequency of the signal provided, rather than relying on the size of the nozzle emitting the droplet. For example, an AIP printer may emit droplets that are magnitudes smaller in size than the orifice openings through which the droplets are emitted. On the other hand, conventional ink jet printing requires a minimization of the nozzle itself to obtain small droplets.
Acoustic ink printheads possess a variety of features that constitute significant distinctions over traditional printheads. For example, ink jet printheads typically have segmented ink reservoirs (or individual ink compartments) for each ink ejector or nozzle. Each compartment also has separate inlets for ink. Similar configurations are found in piezeoelectric and bubble jet type printheads.
Conversely, consistent with the basic functions of acoustic ink printheads as described above, acoustic ink printheads are generally compartmentless printheads that utilize a common pool of flowing ink instead of separate ink compartments. Focusing of a sound beam in such pool is an important feature of acoustic ink printing so the pool of ink is typically very shallow.
In addition, it is desirable to be able to rapidly fill and drain acoustic ink printheads. However, a difficulty in rapidly filling the printhead is that the path through which the shallow pool of ink ultimately flows is very resistive. As such, during filling, there is a high probability that liquid will undesirably escape from the orifices instead of completing a preferred recirculating flow circuit through the printer. Such a preferred recirculating flow circuit involves the flow of ink from an ink reservoir so that it flows to the printhead and over the droplet emitters of the printhead. Of course, select amounts of ink may be emitted as generally described herein but excess ink will preferably flow back to the ink reservoir for re-use. Thus, prevention of this undesired phenomena of ink loss through the orifices and a lack of completion of the recirculating ink flow circuit is important to the filling process. The problem takes on increased significance in view of the fact that a simple acoustic ink printer with recirculating ink flow will not always have power supplied thereto at which time the printhead drains off inkxe2x80x94so the printheads require filling on a regular basis (e.g. each time the printer is turned on).
One contemplated solution is simply to physically block the apertures or orifices from which the ink is emitted. However, the array of apertures is very fragile and pressing on the array might deform the printhead. Any such deformation, no matter how slight, might have a significant impact on print quality. That is, acoustic ink printing requires very precise focusing of sound waves on the surface of the pool of ink. Accordingly, if this surface is moved or altered as a result of deformation of the plate, proper focusing may be negated.
Thus, the present invention contemplates a new method and apparatus for filling and capping an acoustic ink printhead that overcomes the heretofore known difficulties.
A method and apparatus for filling and capping an acoustic ink jet printhead is provided.
In one aspect of the invention, the method comprises aligning/positioning the printhead relative to a capping element, moving a sealing element positioned on the capping element into engagement with the printhead such that the sealing element touches the printhead but transmits substantially no force on the printhead, exerting a force on the sealing element to seal the reservoir such that the force is transmitted to the printhead through the sealing element, establishing ink flow in the printhead, removing the force on the capping element to remove the force on the printhead, and moving the sealing element out of engagement with the printhead.
In a more limited aspect of the invention, the method further comprises selectively opening and closing an air vent valve in the chamber of the capping element.
In another aspect of the invention, the apparatus comprises 1) a plurality of capping elementsxe2x80x94each capping element comprising a first body portion having an air chamber defined therein, a vent valve disposed in the air chamber and a shoulder portion positioned on a periphery of the air chamber, a sealing element positioned on the shoulder, a second body portion upon which the first body portion is resiliently mounted, and a third body portion extending from the second body portion, 2) a base element having a plurality of shaft holes defined therein and a corresponding plurality of shaft collar elements circumferentially aligned to the shaft holes and sized to receive respective shaft portions, and 3) a drive mechanism operatively engaged to the third body portions.
Further scope of the applicability of the present invention will become apparent from the detailed description provided below. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art.